Posed and genuine smiles: an evoked response potentials study.

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Date

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Thesis Discipline

Psychology

Degree Grantor

University of Canterbury

Degree Level

Masters

Degree Name

Master of Science

The ability to recognise an individual's affective state from their facial expression is
crucial to human social interaction. However, understanding of facial expression recognition processes is limited because mounting evidence has revealed important differences between posed and genuine facial expressions of emotion. Most previous studies of facial expression recognition have used only posed or simulated facial
expressions as stimuli, but posed expressions do not reflect underlying affective state unlike genuine expressions. The current study compared behavioural responses and
Evoked Response Potentials (ERPs) to neutral expressions, posed smiles and genuine smiles, during three different tasks. In the first task, no behavioural judgment was required, whereas participants were required to judge whether the person was showing
happiness in the second task or feeling happiness in the third task. Behavioural results indicated that participants exhibited a high degree of sensitivity in detecting the
emotional state of expressions. Genuine smiles were usually labelled as both showing and feeling happiness, but posed smiles were far less likely to be labelled as feeling happiness than as showing happiness. Analysis of P1 and N170 components, and later
orbitofrontal activity, revealed differential activity levels in response to neutral expressions as compared to posed and genuine smiles. This differential activity occurred as early as 135ms at occipital locations and from 450ms at orbitofrontal
locations. There were significant interactions between participant behavioural sensitivity to emotional state and P1 and N170 amplitudes. However, no significant difference in ERP activity between posed smiles and genuine smiles was observed until 850ms at orbitofrontal locations. An additional finding was greater right
temporal and left orbitofrontal activation suggesting hemispheric asymmetry of facial expression processing systems.